That’s the finding of James S. Jaffe, a rare-books expert brought in to review the contents of the safe-deposit box at a bank in Ms. Lee’s hometown of Monroeville, Ala. Mr. Jaffe, who was hired to set the record straight about what’s inside the mysterious box, says that it contains an original typescript of “Go Set a Watchman,” an early typescript of the first third of “To Kill a Mockingbird,” and a later copy-edited typescript of “Mockingbird.”